1. Field of the Invention
The present invention relates to mammalian EPO mimetic hinge core mimetibodies, specified portions and variants specific for biologically active proteins, fragment or ligands, EPO mimetic hinge core mimetibody encoding and complementary nucleic acids, host cells, and methods of making and using thereof, including therapeutic formulations, administration and devices.
2. Related Art
Recombinant proteins are an emerging class of therapeutic agents. Such recombinant therapeutics have engendered advances in protein formulation and chemical modification. Such modifications can potentially enhance the therapeutic utility of therapeutic proteins, such as by increasing half lives (e.g., by blocking their exposure to proteolytic enzymes), enhancing biological activity, or reducing unwanted side effects. One such modification is the use of immunoglobulin fragments fused to receptor proteins, such as enteracept. Therapeutic proteins have also been constructed using the Fc domain to attempt to provide a longer half-life or to incorporate functions such as Fc receptor binding, protein A binding, and complement fixation. One specific and vital role of the mammalian hematopoietic system is the production of erythrocytes, or red blood cells, which transport oxygen to the various tissues of the animal's body. The process of producing erythrocytes (“erythropoiesis”) occurs continuously throughout an animal's life span to offset erythrocyte destruction. The typical red blood cell has a relatively short life-span, usually 100 to 120 days. Erythropoiesis is a precisely controlled physiological mechanism whereby sufficient numbers of erythrocytes are produced to enable proper tissue oxygenation, but not so many as to impede circulation.
Erythropoiesis is now known to be primarily controlled by the polypeptide erythropoietin (EPO), an acidic glycoprotein. Erythropoietin is produced as the result of the expression of a single copy gene located in a chromosome of a mammal. The amino acid sequence for recombinant human EPO (“rHuEPO”) is substantially identical to the amino acid sequence for EPO obtained from human urinary sources. However, the glycosylation of rHuEPO differs from that of urinary EPO and human serum EPO.
In a healthy mammal, EPO is present in the blood plasma in very low concentrations, as the tissues are being sufficiently oxygenated by the existing number of circulating erythrocytes. The EPO present stimulates the production of new erythrocytes to replace those lost to the aging process. Additionally, EPO production is stimulated under conditions of hypoxia, wherein the oxygen supply to the body's tissues is reduced below normal physiological levels despite adequate perfusion of the tissue by blood. Hypoxia may be caused by hemorrhaging, radiation-induced erythrocyte destruction, various anemias, high altitude, or long periods of unconsciousness. In contrast, should the number of red blood cells in circulation exceed what is needed for normal tissue oxygenation, EPO production is reduced.
However, certain disease states involve abnormal erythropoiesis. Recombinant human EPO (rHuEPO) is being used therapeutically in a number of countries. In the United States, the U.S. Food and Drug Administration (FDA) has approved rHuEPO's use in treating anemia associated with end-stage renal disease. Patients undergoing hemodialysis to treat this disorder typically suffer severe anemia, caused by the rupture and premature death of erythrocytes as a result of the dialysis treatment. EPO is also useful in the treatment of other types of anemia. For instance, chemotherapy-induced anemia, anemia associated with myelodysplasia, those associated with various congenital disorders, AIDS-related anemia, and prematurity-associated anemia, may be treated with EPO. Additionally, EPO may play a role in other areas, such as helping to more quickly restore a normal hematocrit in bone marrow transplantation patients, in patients preparing for autologous blood transfusions, and in patients suffering from iron overload disorders.
Erythropoietin (EPO) is a glycoprotein hormone composed of 165 amino acids and four carbohydrate chains that functions as the primary regulator of erythropoiesis by binding to a specific receptor on the surface of erythrocyte precursor cells. This binding signals their proliferation and differentiation into mature red blood cells. The erythropoietin receptor is a 484-amino acid glycoprotein with high affinity for erythropoietin. For the erythropoietin receptor, ligand-induced homodimerization may be one of the key event that governs activation.
Erythropoietin has a relatively short half-life. Intravenously administered erythropoietin is eliminated at a rate consistent with first order kinetics with a circulating half-life ranging from approximately 3 to 4 hours in patients with CRF. Within the therapeutic dose range, detectable levels of plasma erythropoietin are maintained for at least 24 hours. After subcutaneous administration of erythropoietin, peak serum levels are achieved within 5-24 hours and decline slowly thereafter.
Small peptidomimetics of erythropoietin were identified by several groups through screening of random phage display peptide libraries for affinity to the erythropoietin receptor. These sequences have no homology with erythropoietin. In functional assays several of these peptides showed activity, but only 1/100,000th that of recombinant erythropoietin. Although several attempts have been made to increase the potency of these peptides by preparing covalent dimers or multimers of peptidomimetics, these compounds are still 1,000-10,000 fold less active than erythropoietin on a molar basis and have very short half lives that has made them not suitable for use as therapeutics.
Accordingly, there is a need to provide improved and/or modified versions of EPO therapeutic proteins, which overcome one more of these and other problems known in the art.